1. Field of the Invention
This invention relates to photographic elements, and more particularly, to photographic elements used in the field of photographic silver halide photosensitive material containing a high molecular weight matting agent.
2. Discussion of the Prior Art
Photographic elements generally have an outermost or surface layer which contains a hydrophilic organic colloid, typically gelatin as a binder. The surface of the photographic element becomes more adherent and tacky in a high temperature, high humidity atmosphere so that bonding or another failure would often occur when the element is contacted with another object. Such bonding will take place between photographic elements or between a photographic element and another object in contact therewith during preparation, shelf storage, picture taking, processing, and storage after processing, often resulting in serious troubles including blocking of stacked photographic elements, damage to a coating, transfer of a compound from a certain coating to another surface in contact therewith, and electric discharge failure.
Also, photographic elements are often required to have a surface, especially a back surface, which can be marked with a pencil or pen. Neither plastic film supports nor paper supports laminated with polyethylene or another plastic coating can be marked with a pencil or pen irrespective of whether or not they are coated with a binder such as gelatin.
One well-known solution to such problems is to incorporate finely divided material in the uppermost layer of a photographic element to increase the roughness of its surface. The surface is roughened, that is, matted to reduce adhesiveness and to impart writability. The finely divided material is generally known as a matting agent and includes inorganic materials such as silicon dioxide, magnesium oxide, titanium dioxide and calcium carbonate as well as organic materials such as starches, polymethyl methacrylate and cellulose acetate propionate.
These conventional matting agents have several drawbacks. For example, some matting agents adversely affect photographic properties. Some matting agents have a high specific gravity so that they settle in a coating solution, causing a trouble in a coating step during preparation of photographic elements. Some other matting agents are limited in size because of their preparation method and it is difficult to obtain a matting agent of a requisite size.
For the matting agents which are used to impart writability, it is generally known that harder ones are more effective. For the matting agents which are used for anti-adhesion, we have found that harder ones are more effective when anti-adhesion matting agents of the same size are compared. The matting agents which are known to be relatively hard are of inorganic material. Although the inorganic matting agents have a sufficiently high hardness to improve writability and anti-adhesion, they undesirably tend to settle in a dispersion or coating liquid during preparation of a photographic element because of their high specific gravity.
Color diffusion transfer image forming method uses a photographic element having at least one dye-fixing layer for receiving and fixing a mobile dye. Such a photographic element is referred to as a dye-fixing element. When the dye-fixing element is held horizontally in a low humidity atmosphere with its dye-fixing layer faced upward, the hydrophilic colloid in the dye-fixing layer contracts, causing the element to curl such that the opposite edges are bent above the original horizontal plane. When the dye-fixing element is held horizontally in a high humidity atmosphere with its dye-fixing layer faced downward, the hydrophilic colloid in the dye-fixing layer absorbs moisture and thus stretches, causing the element to curl such that the opposite edges are bent above the original horizontal plane. It is known in the art to prevent curling by applying a hydrophilic colloid layer or back layer of a suitable thickness to the surface of a support remote from the dye-fixing layer to thereby offset curling.
The dye-fixing layer often contains a salt such as a base or base precursor, a thermal solvent, or a low molecular weight compound such as a dye transfer aid for the purpose of promoting development of a photosensitive layer and promoting transfer of a dye from a photo-sensitive layer to the dye-fixing layer. Since the hydrophilic colloid (typically a binder such as gelatin) in the back layer is hygroscopic, the salt, thermal solvent or dye transfer aid migrates toward the hydrophilic colloid layer when such dye-fixing elements are stored in a stack. Then the concentration of the salt, thermal solvent or dye transfer aid in the dye-fixing layer lowers, causing a reduction of maximum density (Dmax) or a variation in image density. Adhesion failure occurs particularly when a protective layer generally used in the dye-fixing element is also a hydrophilic colloid layer or contains a similar salt.
Prior art methods for preventing adhesion of photographic elements are by loading a back layer with a matting agent having a particle size of about 1 to about 10 .mu.m as disclosed in Japanese Patent Application Kokai No. 61-205935 or by providing a back layer with irregularities when it is positioned as the outermost layer. However, the former method of loading a matting agent having a particle size of about 1 to about 10 .mu.m is not fully satisfactory, and the latter method of forming irregularities is cumbersome.
There is a need for developing a method capable of overcoming both density variation and adhesion failure.